Synthesis and Anti-Chagas Activity Profile of a Redox-Active Lead 3-Benzylmenadione Revealed by High-Content Imaging

Chagas disease, or American trypanosomiasis, is a neglected tropical disease which is a top priority target of the World Health Organization. The disease, endemic mainly in Latin America, is caused by the protozoan Trypanosoma cruzi and has spread around the globe due to human migration. There are multiple transmission routes, including vectorial, congenital, oral, and iatrogenic. Less than 1% of patients have access to treatment, relying on two old redox-active drugs that show poor pharmacokinetics and severe adverse effects. Hence, the priorities for the next steps of R&D include (i) the discovery of novel drugs/chemical classes, (ii) filling the pipeline with drug candidates that have new mechanisms of action, and (iii) the pressing need for more research and access to new chemical entities. In the present work, we first identified a hit (4a) with a potent anti-T. cruzi activity from a library of 3-benzylmenadiones. We then designed a synthetic strategy to build a library of 49 3-(4-monoamino)benzylmenadione derivatives via reductive amination to obtain diazacyclic benz(o)ylmenadiones. Among them, we identified by high content imaging an anti-amastigote "early lead" 11b (henceforth called cruzidione) revealing optimized pharmacokinetic properties and enhanced specificity. Studies in a yeast model revealed that a cruzidione metabolite, the 3-benzoylmenadione (cruzidione oxide), enters redox cycling with the NADH-dehydrogenase, generating reactive oxygen species, as hypothesized for the early hit (4a).

Synthesis and Photochemical Properties of Fluorescent Metabolites Generated from Fluorinated Benzoylmenadiones in Living Cells

This work describes the reactivity and properties of fluorinated derivatives (F-PD and F-PDO) of plasmodione (PD) and its metabolite, the plasmodione oxide (PDO). Introduction of a fluorine atom on the 2-methyl group markedly alters the redox properties of the 1,4-naphthoquinone electrophore, making the compound highly oxidizing and particularly photoreactive. A fruitful set of analytical methods (electrochemistry, absorption and emission spectrophotometry, and HRMS-ESI) have been used to highlight the products resulting from UV photoirradiation in the absence or presence of selected nucleophiles. With F-PDO and in the absence of nucleophile, photoreduction generates a highly reactive ortho-quinone methide (o-QM) capable of leading to the formation of a homodimer. In the presence of thiol nucleophiles such as β-mercaptoethanol, which was used as a model, o-QMs are continuously regenerated in sequential photoredox reactions generating mono- or disulfanylation products as well as various unreported sulfanyl products. Besides, these photoreduced adducts derived from F-PDO are characterized by a bright yellowish emission due to an excited-state intramolecular proton transfer (ESIPT) process between the dihydronapthoquinone and benzoyl units. In order to evidence the possibility of an intramolecular coupling of the o-QM intermediate, a synthetic route to the corresponding anthrones is described. Tautomerization of the targeted anthrones occurs and affords highly fluorescent stable hydroxyl-anthraquinones. Although probable to explain the intense visible fluorescence emission also observed in tobacco BY-2 cells used as a cellular model, these coupling products have never been observed during the photochemical reactions performed in this study. Our data suggest that the observed ESIPT-induced fluorescence most likely corresponds to the generation of alkylated products through reduction species, as demonstrated with the β-mercaptoethanol model. In conclusion, F-PDO thus acts as a novel (pro)-fluorescent probe for monitoring redox processes and protein alkylation in living cells.